In order to protect legal rights of the content owner, the DRM manages use of digital contents through a content protection and permissions control solution.
A typical DRM solution includes: A Content Issuer (CI) uses a Content Encryption Key (CEK) to encrypt digital contents and encapsulate them into a DRM Content Format (DCF), distributes them to the devices, and sends the content identifier of the digital contents and the corresponding CEK to the Rights Issuer (RI). The RI generates a license corresponding to the digital contents, and sends the license to a DRM agent in the device. The license includes the CEK, and the rights and limitations of using the contents. The rights include execution, playing, and moving; and the limitations include use count, accumulated time, and validity period. After obtaining the DCF and the license, the DRM agent obtains the CEK through decryption, obtains the contents through decryption, and uses the digital contents according to the permissions specified in the license.
The SRM is a kind of removable medium that protects internal data against unauthorized access. With the SRM storing and moving the DCF and the license, the storage space is expanded, and the license is movable.
In certain scenarios, the subscriber expects to present the license to others or replace the SRM, which involves moving or copying of the license from one SRM to another SRM. With the popularization of multi-card-in-one-phone, subscribers have more requirements of sharing licenses between SRM cards.
The SRM standard of the Open Mobile Alliance gives protocols for moving a license from a device to an SRM, and moving a license from an SRM to a device. The SRM agent is an entity for performing DRM-related functions in the SRM.
The prior art provides a solution to moving a license from a DRM agent to an SRM, and a solution to moving a license from an SRM to a DRM agent. In both of the solutions, the sharing permissions are deducted after every moving operation. If a license needs to be moved from SRM1 to SRM2, the license needs to be moved from SRM1 to the DRM agent first, and then from the DRM agent to SRM2, which involves at least two deductions of the sharing permissions. However, the prior art has the disadvantage that the moving of a license involves multiple deductions of permissions, which is a waste of permissions to the subscriber.